RIGA — British Prime Minister David Cameron used his first post-election summit with his fellow European Union leaders Friday to breach the subject of changes to the way the bloc works ahead of a referendum before the end of 2017.

“We need to address the concerns of the British people,” Cameron told reporters after meeting with European Council President Donald Tusk. “They are not happy with the status quo, and frankly neither am I.”

Riga is just the start of a broader diplomatic offensive, the result of a pledge made by Cameron before his unexpected victory in UK elections earlier this month. The UK premier meets French President François Hollande next week, and has invited European Commission President Jean-Claude Juncker to Chequers, his rural retreat, on Monday.

The idea is to open the subject of substantial reforms to the EU, changes deep enough that would allow Cameron to campaign in favor of staying in the union in the in-or-out referendum he has called for 2017 at the latest.

The most pressing issue, the prime minister said, is “the huge increase in people migrating to the UK from Europe and the fear that we can do nothing to address it.” He cited the figure that one in eight Lithuanians lives in his country and mentioned “the very generous way that you can access our welfare system and our in-work benefits … almost on day one within arriving.”

But challenging the EU’s freedom of labor mobility will prove problematic for heads of government on the continent and create a double standard for EU migrants in the UK; it is certain to rankle central and east European leaders. Lithuanian President Dalia Grybauskaitė pointedly said Friday that freedom of movement within the EU was a “core value.”

The Eastern Partnership summit was aimed primarily at discussing the EU’s relationship with six ex-Soviet republics — Moldova, Ukraine, Georgia, Azerbaijan, Armenia and Belarus. But European leaders have capitalized on the fact that most of the bloc’s heads of state and government are in the Latvian capital to push their own issues.

“These talks will not be easy. They will not be quick. There will be different views and disagreements along the way. But by working together in the right spirit and sticking at it, I believe we can find solutions that will address the concerns of the British people and improve the EU as a whole,” Cameron said in a statement upon arriving in Riga.

Cameron wants to push through the referendum before the European political calendar becomes clogged by elections in Germany and France in 2017. But his demand to renegotiate EU treaties may be too time-consuming and complex as those changes have to be accepted by 27 other member states.

“I don’t know what he is asking for,” said Martin Schulz, president of the European Parliament. “Not everything has to be done in Brussels. I agree entirely. This is feasible without a treaty change. I think the overwhelming majority of the member states of the EU know there will be a lot of obstacles for treaty change…. You need a ratification in 28 countries. It will take a lot of time.”

But simply tweaking regulations and laws may make it difficult to demonstrate to the Britons who elected him that he has deeply reformed the Union.

Cameron is not underestimating the difficulty in striking an acceptable deal.

“I’m not going to say I was met with a wall of love when I arrived,” he said. But he didn’t shy away from his right to push for changes to the Union. “The way Europe works is if a country has a problem or a difficulty you should be able to put it on the table and talk about it.”

And once that’s done, “The British people will have the final decision,” he said.